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Proceedings of an International Conference on Mitigation of Heat Exchanger Fouling and Its Economic and Environmental Implications

ISSN:
1-56700-172-6 (Print)

MODELLING OF CRYSTALLINE SCALE REMOVAL

C.J. Wilson
Department of Chemical Engineering University of Cambridge Pembroke Street Cambridge CB2 3RA, UK.

P.R. Lockyer
Department of Chemical Engineering University of Cambridge Pembroke Street Cambridge CB2 3RA, UK.

D. I. Wilson
Department of Chemical Engineering University of Cambridge Pembroke Street Cambridge CB2 3RA, UK.

Abstract

The removal of crystalline scale deposits from stainless steel surfaces has been studied experimentally using dilute solutions of hydrochloric acid to remove thin layers of calcium carbonate (calcite) in a purpose built flow cell. The initial linear removal rate decreased rapidly after a point which corresponded to the appearance of scale-free patches on the metal surface. Modelling the removal rate required reliable values of the surface-liquid mass transfer coefficient, which were obtained from heat transfer measurements. Modelling studies indicated that diffusion of H+ was the rate controlling step for the range of Re considered (2000 < Re < 5000). The overall cleaning behaviour was found to be dominated by the roughness and non-uniformity of the deposit.